1. Field of the Invention
The present invention relates to the field of dredging of sediment, and in particular to a permanently-installed dredging system in which periodically-activated suction is applied to a novel drain structure mounted at a desired depth to withdraw sediment accumulating above such depth.
2. Description of the Prior Art
Sediment removal systems in which suction conduits are mounted below a desired level of sediment have been attempted previously. U.S. patents to Schoonmaker including U.S. Pat. Nos. 3,638,432, 4,074,535 and 4,147,450 teach variations of a system in which a horizontally-oriented suction conduit is bored at spaced point along an upper side to form a series of openings into which sediment is theoretically drawn when a suction pump is actuated. The Schoonmaker devices have no particular intake structure; the horizontal tube is merely vertically bored at spaced points along its length. In order to prevent problems of clogging or jamming due to sediment accumulation over the spaced apertures, Shoonmaker provides an auxiliary water conduit fed from an input located in the water, well above the level of sediment. Auxiliary spray heads around the intake are activated when suction commences, to agitate and entrain the sediment together with water and form a slurry to be drawn in. The apertured tubes are aligned to extend transversely across a stream or the like at spaced areas. Another example of a linear system using straight conduits having intakes on atop side is shown in a patent to Gaylord, U.S. Pat. No. 3,013,395, and also employs auxiliary spray means to agitate and entrain sediment.
The prior art also has conceived of using simple depressions in a watercourse in order to accumulate sediment, thereby clarifying the water in the watercourse or retarding accumulation of sediment elsewhere. Examples of sandtraps for accumulating sediment are shown in U.S. Pat. Nos. 552,877--Ipson and 2,673,451--Gariel. In these disclosures, depressions having sloping sides are formed in the bottom of the watercourse, and the depressions terminate in a conduit. In Gariel, a plurality of baffles are provided to reduce turbulence in the water and thereby allow the sediment to settle and accumulate. In Ipson, the depression itself is apparently considered sufficient to slow the water and accumulate sediment. In Ipson, a displacable drain plug may be removed using an apparatus reaching to the surface of the water, allowing the sediment to be discharged, together with water.
The Ipson device may be characterized as a depression across the bottom of the channel which may be flushed when full. In modern use, large scale sandtraps in the form of dredged-out depressions at or adjacent navigable channels are employed to retard accumulation in the channel. These formations are based upon the fact that sediment is at least partly mobile, and will accumulate first in the area of lowest elevation. Therefore, one approach to maintaining the bottom of a watercourse below a predetermined point has been to provide a deep depression which fills up with sediment before substantial sediment can accumulate in the balance of the channel or watercourse area. The sandtrap depression must then be dredged instead of the channel, or in addition thereto.
In U.S. Pat. Nos. 1,986,148 and 2,422,358, both to C. B. Harp, a conduit system having a particular mounting structure for auxiliary pressure nozzles is disclosed. As in Schoonmaker, the object of the nozzles is to agitate and entrain sediment around the intake head in order to allow a flow of a slurry of sediment and water. In Harp, the nozzles are positioned in a protected enclosure, namely under a conical hat carried by spaced supports attached to a conduit.
Aside from the matter of dredging, conical fittings for conduit intakes have been used for various purposes. For example, in U.S. Pat. No. 1,482,216--Boosey a conical intake having a grate thereupon leads from an external area into a drain conduit. The conical intake is provided in order to increase the cross-section exposed to flow in the area of the grate, and thereby decrease the likelihood that the grate will become clogged.
The present invention differs from such prior art use of conical intakes because rather than decrease the concentration of obstructing materials, the invention concentrates and accumulates sediment at an entry point. In so doing, the entire cross-section of water defined by the flared or conical funnel-shaped opening acts upon the localized sediment accumulating at the narrowest part of the intake, forcing the sediment to flow into the conduit system, Moreover, the invention forms a horizontal flow of water around the intake to draw peripheral accumulation into the intake. The intake and drain action is also driven by a discharge side of the suction pump which is preferably mounted at the same elevation as the intake, such that the fluid head over the accumulated sediment offsets the output head on the suction pump in lifting and discharging the fluid and entrained sediment.
Unlike prior art sandtraps, the invention comprises a plurality of intakes that are spaced in two or even three dimensions to define a desired depth for the bottom of the watercourse in that area. Each intake is quite broad, and just steep enough that any sediment falling on the intake slides down the sloping intake walls to accumulate immediately adjacent the intake opening. The intake walls are thereby kept as horizontal as practicable, and help define a horizontal direction of flow into the intake. The horizontal flow entrains sediment surrounding the intake, bringing the depth surrounding the intake to a level closer to that of the intake. Accordingly, occasional operation of the suction pump is all that is necessary to clear the intake of sand and/or any accumulated sediment and also to remove peripheral accumulations. No auxiliary agitators are required. The invention accomplishes this while minimizing the need for suction pump capacity, because the conduit system is valved at the intakes such that pump capacity is controllably concentrated on individual intakes or sets of individual intakes.